A solid-state image pickup device (hereinafter also simply referred to as an “image pickup device”) is obtained by forming an image sensor and an optical element such as a microlens on a semiconductor substrate (hereinafter referred to as a “wafer”) and hermetically sealing them and is used as a light-receiving sensor for video equipment such as a video camera, digital camera, or mobile phone camera.
For the purpose of reduction in size and increase in density, image pickup devices of recent years adopt a packaging technology called “wafer level chip size packaging (hereinafter also simply referred to as “wafer level CSP”)” for completing a wiring step and a step of bonding a protective member before cutting a wafer and cutting the wafer into chips for chip formation (hereinafter referred to as “separation into individual pieces”) (e.g., Patent Documents 1 and 2).
A conventional solid-state image pickup device which uses wafer level CSP generally has a flat transparent plate (transparent flat plate) above a light-receiving portion of an image sensor. The transparent plate is joined to a partition portion (rib) which surrounds the light-receiving portion on four sides with adhesive whose viscosity is appropriately adjusted, and the light-receiving portion including an optical element such as a microlens is hermetically sealed in a void formed between the rib and the transparent plate (Patent Documents 1 to 4).
Note that there is also available a solid-state image pickup device which does not use wafer level CSP, includes a transparent resin film having a flat interface on a microlens instead of a transparent plate, and exhibits an aspect of a microlens characterized in that the relation 1<n1<n2 holds, letting n2 be the refractive index of the microlens and n1 be the refractive index of the transparent resin film (Patent Document 5).    Patent Document 1: Japanese Patent Laid-Open No. 2003-163342 (e.g., FIGS. 2 and 7)    Patent Document 2: Japanese Patent Laid-Open No. 2005-285848 (e.g., FIGS. 2 and 3)    Patent Document 3: Japanese Patent Laid-Open No. 2001-351997 (e.g., FIG. 1)    Patent Document 4: Japanese Patent Laid-Open No. 2002-329850 (e.g., FIG. 2)    Patent Document 5: Japanese Patent Laid-Open No. 2005-316111 (e.g., FIG. 1)
However, in the case of a structure which has a transparent plate above a light-receiving portion, since the transparent plate and a rib are bonded together with adhesive, an insufficient amount of adhesive leads to a problem in terms of long-term reliability. More specifically, the adhesion is insufficient, an external shock weakens the joining strength, and the transparent plate and rib are disjoined after long-term use. On the other hand, use of a large amount of adhesive may lead to intrusion of excess adhesive into the light-receiving portion (hermetically sealed region) adjacent to the rib and degrade the optical properties.
For this reason, conventional wafer level CSP has low long-term reliability or low production yield. Even if the amount used of adhesive is appropriate, a solid-state image pickup device which uses conventional wafer level CSP is susceptible to an external shock, and no provision is made against shocks.